Many process steps in the manufacturing of semiconductor devices are conducted in a vertical furnace. A typical vertical furnace system may include a wafer load/unload system which includes a stack of semiconductor wafers and a robotic arm to remove individual wafers from the stack and to load the wafers into a quartz boat. The quartz boat may include a plurality of support arms that extend outwardly from a platen and are designed to hold the semiconductor wafers in a vertically spaced apart arrangement. The platen may have a through hole formed therein. Process byproduct gases may be exhausted through the through hole in the platen and into a conduit so that process waste gases from the vertical furnace can be removed. A quartz boat motor drive system may be provided to raise and lower the quartz boat into and out of the vertical furnace.
The vertical furnace typically includes a quartz bell jar and a quartz inner tube. Heating elements are typically provided on the outside the other quartz bell jar. Process gases are charged through an opening in the quartz bell jar and down into the inner tube and flow over the semiconductor wafers that are in the vertically spaced apart positions in the quartz boat.
The inner tube may have a variety of different configurations depending upon the type of process to be conducted in vertical furnace. For example, the diameter of the inner tube used in the TEOS process may be substantially smaller than the diameter of an inner tube used in a silicon nitride or polysilicon process. Furthermore, the outer and inner tubes may have to be disassembled from each other to clean these components and remove any deposits formed thereon from various processes conducted in the furnace. Upon assembly of the bell jar and the inner tube, often it becomes difficult to properly center of the inner tube with respect to the outer bell jar. Failure to properly center the inner tube with respect to the bell jar may result in a uniformly problem wherein the deposition or growth of a desired material on the semiconductor wafer may have a greater or lesser thickness near the edge of the semiconductor wafer that is closest to the bell jar. This uniformly problem is believed to be due to the fact that one of the edges of the semiconductor wafer is positioned closer to the heating elements surrounding the bell jar and/or the flow of process gases is restricted at the edge of the wafer closest to the bell jar. Thus it would be desirable to provide a vertical furnace calibration tool and a method of using the same to properly center the inner tube with respect to the outer bell jar and to ensure uniformity of deposition or growth of materials over the entire surface of the wafer.